1. Technical Field
A method for manufacturing a semiconductor device is disclosed, that is capable of securing the stability in a polishing process for forming a landing plug.
2. Discussion of Related Art
Generally, a polishing process is performed for an electric isolation of word lines at the time of manufacturing a semiconductor. However, after the polishing process, an insulator film is over-dished due to differences of an etching rate between the insulator film deposited for insulating of the word lines and a poly silicon film for a landing plug (hereinafter also referred to as a “LP”). Thereby, slurry residues generated during the polishing process become to remain on an upper face of the insulator film over-dished. The aforementioned slurry residues are mostly composed of metal materials having electric conductivity, and they come to remain as they are because it is difficult to remove them through the following cleaning process. The residues, as described above, affect the electric separation of word lines, seriously.
The latest technologies decrease the polishing amount on the process to during the polishing process. However, in such a case, there are many problems in the electric separation of word lines, relatively. The reason is that the word lines of regions to be opened on forming a landing plug contact for LP are more attacked relatively than the other regions not to be opened, whereby the profile of upper word lines changes into a round shape. Therefore, the upper area of LP becomes to be larger and the electric separation margin of word lines gets more deteriorated. Though the polishing amount is increased again at the time of the polishing process to overcome these problems, the residual nitride film of word lines becomes to decrease, whereby the process of forming storage nodes and bit line self align contacts is affected and, furthermore, the short between these and tungsten silicide of word line would be generated.